Ultra

Voice format: Telnyx.Ultra.<voice> Sub-100ms latency. 36 languages.

REST only — Ultra is not available over public WebSocket.

Voice Samples

Voice	Language	Gender
`Telnyx.Ultra.Asher`	en	Male
`Telnyx.Ultra.Callie`	en	Female
`Telnyx.Ultra.Clara`	en-US	Female

Expressive Mode for AI Assistants

Enable Expressive Mode when using an Ultra voice with AI Assistants. The assistant can select emotion tags and nonverbal cues from the conversation context without hard-coding each expression in the system prompt. For example, an assistant can use an excited tone for good news, respond empathetically to a problem, insert [laughter] in a friendly exchange, and keep routine information neutral.

Conversation transcript showing an AI assistant selecting Ultra emotions and laughter from the conversation context

Enable in the portal

Open the assistant in the Telnyx Portal.
Under Voice Settings, select a Telnyx.Ultra.* voice.
Enable Expressive Mode.
Save the assistant.

AI Assistant voice settings with a Telnyx Ultra voice and Expressive Mode enabled

Enable via API

Set expressive_mode: true in the assistant’s voice_settings:

curl -X PATCH "https://api.telnyx.com/v2/ai/assistants/YOUR_ASSISTANT_ID" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "voice_settings": {
      "voice": "Telnyx.Ultra.YOUR_VOICE_ID",
      "expressive_mode": true
    }
  }'

expressive_mode requires a supported expressive voice. Use a Telnyx.Ultra.* voice for Ultra Expressive Mode.

SSML Emotions

Ultra supports inline SSML emotion tags. Place the tag before the text:

<emotion value="excited" />Great news — your order shipped early!

Primary emotions: angry, excited, content, sad, scared. Additional: happy, enthusiastic, curious, calm, grateful, affectionate, sarcastic, surprised, confident, hesitant, apologetic, determined, frustrated, disappointed. Omitting the tag = neutral delivery. Use sparingly — Ultra interprets emotional subtext from the text itself.

Nonverbal Cues

Insert [laughter] inline for natural laughing:

That's hilarious! [laughter] Anyway, let me check your account.

Language Support

Set language_boost to improve pronunciation for the target language: Arabic, Bengali, Bulgarian, Chinese, Czech, Danish, Dutch, English, Finnish, French, German, Gujarati, Hebrew, Hindi, Indonesian, Italian, Japanese, Korean, Malay, Marathi, Māori, Norwegian, Polish, Portuguese, Punjabi, Romanian, Russian, Slovak, Spanish, Swedish, Tamil, Telugu, Thai, Turkish, Ukrainian, Vietnamese.

REST API

Fields

Field	Type	Default	Description
`voice_speed`	float	`1.0`	Speech rate multiplier.
`language_boost`	string	—	Target language hint.
`volume`	float	—	Output volume.
`emotion`	string	—	`neutral`, `happy`, `sad`, `angry`, `fearful`, `disgusted`, `surprised`.
`sampling_rate`	integer	—	Output sample rate in Hz.
`output_type`	string	`binary_output`	`binary_output`, `base64_output`, or `audio_id`.

Response

Default (binary_output): chunked audio bytes with Content-Type: audio/mpeg. With output_type: "base64_output": JSON with base64-encoded audio. With output_type: "audio_id": JSON with an audio_url for deferred retrieval.

WebSocket Streaming

REST API

Providers

Other

API Reference

For AI Agents

Voice Samples

Expressive Mode for AI Assistants

Enable in the portal

Enable via API

SSML Emotions

Nonverbal Cues

Language Support

REST API

Fields

Response

See also

​Voice Samples

​Expressive Mode for AI Assistants

​Enable in the portal

​Enable via API

​SSML Emotions

​Nonverbal Cues

​Language Support

​REST API

​Fields

​Response

​See also

Voice Samples

Expressive Mode for AI Assistants

Enable in the portal

Enable via API

SSML Emotions

Nonverbal Cues

Language Support

REST API

Fields

Response

See also